This invention relates to sealing gaskets and more particularly to a tandem seal arrangement intended to address multiple problems associated with highly corrosive process media or high purity requirements, and situations requiring heat resistant characteristics. The invention finds particular applicability in annular gasket arrangements that are disposed between pipe flanges provided at opposite ends of pipe sections. The pipes or fluid lines are often used in the petroleum, petrochemical, nuclear, and other related industries, although the subject invention may be useful in other environments and applications.
Spiral wound gaskets are well known in the industry. Typically, a spiral wound gasket includes a metal strip between which strips of a sealing material are interspersed as the strip is wound upon itself forming an annulus about a central axis. By way of example only, a number of different metals can be used for the metallic winding such as stainless steel, monel, nickel, titanium, or carbon steel. Each material provides its own particular characteristics to meet desired specifications. Likewise, various filler materials can be used. Typically, the filler material employed is a softer strip of material that is deformed when compressed between the pipe flanges providing desired sealing characteristics.
As indicated above, spiral wound gaskets are normally disposed between opposed flanges of mating pipe ends. The pipe flanges are clamped together by means of circumferentially spaced bolts or any other suitable fastening arrangement. In selected situations, radially inner and/or outer guide rings may be used in conjunction with the spiral wound gasket. The guide rings are usually formed from carbon steel and serve a number of different functions in the gasket assembly. A primary function of the outer guide ring is to act as a compression limiter. Additionally, the outer guide ring provides increased radial strength to the gasket assembly. Moreover, the outer guide ring facilitates installation, in addition to providing a positive centering of the gasket on the pipe flange. The inner ring protects against distortion of the gasket, limits erosion of the pipe and flange faces, and also protects the gasket from adverse effects associated with excessive turbulence.
A particular need in various industries exists for a gasket or seal assembly that serves dual purposes. A fluid system may have two primary functions that need to be addressed. For example, highly corrosive process media oftentimes attack gasket materials thereby requiring more frequent maintenance and/or replacement. Likewise, other applications require high purity thus precluding use of less expensive gasket filler materials that might contaminate the process media.
Still another primary goal is to provide a radially outer seal that is heat resistant. The heat resistant seal is intended to maintain seal integrity for a predetermined time period if the gasket assembly is exposed to elevated temperatures associated with extreme heat or fire. Oftentimes, the radially inner seal that is intended to address the high purity or high corrosive problems results in use of a seal material that is particularly sensitive to elevated temperatures. Thus, the outer seal is designed to act as a seal if exposure to elevated temperatures occurs.